Method of preventing the rusting of iron and steel.



U IT D STATES- PATENT OFFICE.

DANIEL F. COMSTOGK, OF BROOKLINE MASSACHUSETTS, ASSIGNOR TO COMSTOCK &

WESCOTT, INCORPORATED, OF BOSTON, MASSACHUSETTS, CORPORATION OF MAS-SACHUSETTS.

No Drawing.

To all whom it may mm Be it known that I, DANIEL F. CoMs'rooK,

. a citizen of the United States, residing at Brookline, in the countyof Norfolk and State of Massachusetts, have invented cer- It is wellknown that iron or steel will be attacked by rust if exposed to Watenora moist atmosphere. Such rusting is particularly destructive tostructural iron work so that to preserve it various methods have beenproposed to prevent the attacks of rust. The usual method of protectingiron and steel is to coat them with various kinds of paint.- Theaimof'painting in all cases has been to exclude moisture from the metalsurface.

When the rolled iron and steel comes from the rolling mill, its surfaceis covered with a black oxid known as ,mill bloom which does not rust.The usual method of protecting the iron or steel is to paint it at-themill with the common red lead linseed-oil paints. Usually the paint isspread over the surface which is more or less covered with the bloomfrom the rolling'mill. This bloom, because of its different coefficientof expansion, in time becomes loosened from the underlying metal andopens upminute cracks so that moisture is able to penetrate through thecracks in the paint beneath the edges of the bloom scales and attack themetal beneathl The resultant rust working beneath the scales of bloomloosens them so that in time they peel off and. expose the naked metal.On account of the peeling of the bloom scales, it is considered thebetter, although the much more expensive, practice to remove the bloomfrom the iron or steel before painting at the mill. This is donemechanically by means of a sand blast, brush, hammer, or chisel, orchemically by means of acid baths. After the surfaces have been cleaned,they are painted at the mill before the iron or steel is shipped. Theamount ,of protection against rust obtained Specificationof LettersPatent.

Application filed June 2, 1911. Serial No. 630.879.

METHOD OF PREVENTING THE RUSTING IRON AND STEEL.

' Patented Nov. 9, 1915.

by-such treatment depends upon the clearness and dryness of the surfaceand the imperviousness of the paint films applied.

Aside from the objection of expense 'in-. volvedin such treatment, it isfound almost. imposslble, except by the exercise of the highest degreeof care, to free the iron or steel surface from oxid or moisture and to,

keep it free before the paint is applied. The paint film is relied on toprevent the access of moisture to the underlying metal. It is well knownthat paint films seldommeasure more than a fewthousandths of an inch inthickness and that even the best paint film is not entirely impervious--to moisture. Whether this is because the paint, while drying,contracts and the contraction opens up 7 little pores or cracks in thefilm, or because the dried film, when subjected to moisture,

forms a semi-solid solution through which the moisture' 'penetrates bydiffusion to the surface of the metal, is not known, but it is knownthatunless the surfaceof the metal was free from oxid and moisturebefore the paint was applied,-tha-t'in time rustingwill take. placebeneath'the paintfilm.

Afterthe metal sheets or'beams have been assembled in the: building,bridge, or ship, a

second coatof paint is usually applied to all of the exposed surfaces.Where the surfaces are left permanently exposed, as on the exposed partsof bridges or the outside of ship plates, new coats of paint are appliedfrom time to time where the original paint has flaked oil and thus thelife of the structure is prolonged. This cannot be done when the metalis inclosed in the building materials as, for instance, by being boxedin by a stone, brick, terra-cotta, or concrete sheath, so that theoriginal paint coats are the only protection the iron or steel hasagainst moisture coming through itsinclosing sheath.

' All iron or steel structures are made up of a number of membersriveted or bolted together which are in turn often compound piecesthemselves. The units making up the members are so riveted together thata considerable part of the surface of one is 0pposed to that of another.The integrity of the members depends on the bond'between the unitseffected by the contraction of the rivets oncooling. Since the rivetedor bolted joints are generally made before the second coating of paint,their inner opposed sur- .rust.

. of the oxid over the original volume of iron from which it is formed.The pressure, due to the swelling or chemical increase inthe volume ofthe rust between the members, has been known to have become great enoughto shear off the heads of the rivets and'destroy the joint. This rustingon the inaccessible surfaces of riveted joints is particularlydestructive in its operation on marine structures such as steel ships.Here the constant vibration and the presence of a large amount'ofmoisture, whichinevitably is diffused through the riveted joints, tendsto destroy them very rapidly.

Iron and steel are extensively used as reinforcing material forconcrete. When so em.- ployed, the metal bars are generally cleaned to amore or less extent with a sand blast or wire brush and the concretemixture poured and tam ped about them. The best Portland cement concreteis at most but a more or less porous sheath for the embedded iron orsteel bars. It is well known that it is exceedingly difficult to makeconcrete even approximately water tight. It is found that in old reinforced concrete work, particularly if it has been exposed to water or ahumid atmosphere, the bars have been more or less attacked by rust. Thisrust destroys the bond between the concrete and the bars and so lessensthe strength of the structure. More over the phenomenon of swelling ofrusted bars may be'particularly destructive. In certain instances thisswelling of the iron bars by rust has become so great that the concretehas actually. been burst or disrupted by the rusting of the embeddediron bars. It is at present the general custom to embed the iron barsdirectly in the concrete without any special protection and trust thatthe preliminary cleaning of the bars and the conditions under which theconcrete is used maybe favorable enough to keep the bars from any veryrapid deterioration. by rustmg.

It is well known that if the surfaces of the iron or steel are keptabsolutely; dry, no rusting will occur. The presence of moisture is oneof the essential conditions for the chemical phenomenon known asrusting.Of the various theories which seek to explain the chemical action, theso-called electrolytic theory is the most generally accepted and isbelieved to ofier the correct explanation.

rium, the hydrogen ions of the solution migrate to the surface of theiron and give up their positive charges. Thus, according to theelectrolytic theory, it is necessary that moisture be present to allowthe iron to pass into solution and that the water or moisture must besufficiently impure so that it will act as an electric conductor andmust also be in such condition that hydrogen ions are pres cut. Thiselectric local battery action is greatly assisted by the presence ofimpurities, such as rust, at the surface of the iron, because theimpurities or rust are of a different potential with respect to thesolution than the pure iron, so that a localbattery circuit is set upthrough the solution between the pure iron surface and the rust orimpurities. This assistance to electric action given by the rustprobably explains why the surfaces, which are somewhat rusted beforepaint is applied, rust more rapidly than surfaces which are absolutelyclean before the paint is applied, because the rust tends to set up alocal battery action through the moisture which has penetrated throughthe paint to the iron surface or which is diffused in the paint in asort of semi-solid so lution. Theoretically, therefore, there are twoways in which to prevent rusting. First, by absolutely excludingmoisture from the surface and, second, by rendering the'water ormoisture incapable of acting as an electrolyte to support the localbattery action at the iron surface. While iron will rust in im-" purewater, particularly if the. water contains acid and if there are alreadyincipient rust spots on the surface, yetif a certain amount of alkali bepresent in the water abs solutely no rusting will take place even thoughthe iron surface has been rusted before being placed in the alkalinesolution.

The probable explanation of the inhibitire effect of the alkali onrusting is that the presence of the alkali prevents such aconcentration. of the free hydrogen ions in the solution as to allow itto act as an electrolyte to decompose the iron.

The action of the alkali in preventing a. concentration of free hydrogenions in solution. is the same chemical action which causes the alkali toneutralize an acid, therefore the alkaline carbonates, as well as themains and has been proved by many experiments that iron which is inintimate contact with an alkali will not rust.-

The essential condition in preventing rust is that the alkali must beintimately associated with the entire surface to be preserved fromrusting. Thus, a piece of iron tion which is the cause of the rusting.If,

on the other hand, the entire surface is not impregnated withthe'alkali, rusting may occur at portions of the surface where for somereasonthe alkali is prevented from impregnating the metal surface. It isbelieved that the well known phenomenon of the rusting of ironcontainers of alkali after they are opened to the air and moisture, is

due to the fact that. there are present on the container surface placeswhere, due to the presence of organic matter, scale or the like, thesurface is not in intimate contact with the alkali. At such placesrusting may occur, giving rise to the characteristic mottled appearanceof the container surface when the rusting first occurs, and these rustcenters may eat into the metal until the container is rendered useless.As above stated, this action is believed to be due to the rusting firstset up at portions of the surface which are not alkali-impregnated andat which free hydrogen ions can and do exist to formv local rust centerswhich spread into the metal. This condition of local uniinpregnated rustcenters is to be contrasted with a condition in which the entire surfaceis so treated with alkali that it is completely and thoroughlyimpregnated and no unimpregnated places exist to later form local rustcenters. \Vit'h the object, therefore, of preventing iron and steel fromrusting, the present invention consists in a method of preventing rustby the means of an alkali, and particularly by so treating the iron orsteel that the alkali is maintained in intimate contact with the entiresurface to be preserved. The present invention contemplates utilizingthe rust preventing and arresting qualities of an alkalion a commercialbasis for preserving iron and steel.

The present invention in* one of its broader aspects contemplatestreating the surface to be preserved with an alkali in such a mannerthat the alkali is etained at the surface after the treating operationis completed.

The present invention contemplates as another featurefthe treating ofthe surface with an alkali and the subsequent sealing in,

or coating of, the surface to exclude moisture as much as possible, theexclusion of moisture being to exclude water as one of the rustcontributing agents and also, what is fully as important, the exclusionof the water to prevent its washing the alkali from the treated surface.

The present invention is susceptible of being practised in a number ofspecific modes of procedure since the essentials of the inventionconsist in applying the alkali to the surface of the iron or steel andin the employment of a; suitable retaining agent or means to keep itthere to inhibit rusting.

For convenience in disclosing various ways in which the presentinvention may be practised, the. preferred methods of preventing rust onsuch surfaces as are exposed in the structure after the iron Work isassembled and which are usually covered with the second coating ofpaint, such surfaces as are covered over with an embedding sheathlikeconcrete, and such surfaces as lie between theriveted and boltedjoints of the iron structure, which cannot be reached by the usualsecond coat of paint,

will be discussed.

Surfaces which may be painted after the iron or steel structure 2'saesembled.After the iron pieces come from the rolling mill, it ispreferable not to give them the usual coat of' red lead linseed-oilpaint, but to erect the iron posts, girders or plates without anytreatment. The action of moisture and gases will tend to loosen the millbloom from the iron surface so that by brushing most of the scale may betaken off. The exposed surfaces will then be clear from scale andalthough rusted somewhat most of the loose rust will be brushed off. Thesurfaces are then to be painted over with an alkali dissolved in asuitable solvent. A microscopic examination of any iron or steel surfacewill "reveal the fact that the surface is not continuous or solidbut isliterally honeycombed with minute pores and crevices. The solvent actsto carry the alkali into the minutest pores and crevices of the surfaceso that not only is the surface covered with alkali but the surfacelayer of the iron itself is thoroughly impregnated by the alkali. Thesurfaces are exposed until the solvent is evaporated, and, in case thealkaliis applied as a hydrate, until the carbon, dioxid in the airchanges the hydrate into a carbonate, and the alkali is left as acarbonate. Then the iron is painted over with a coating which is notprejudicially affected by the alkali and which will act' both as aninert holder to keep the chemically active alkali on the surface, and inthe pores of the iron to prevent future rusting and as a protectingthose at present in vogue.

To insure a better mechanical protectionagainst abrasion or weather,subsequent coatings of paints or varnishes may be applied. It isobvious, however, that these may be of any kind since the inner alkaliresisting coating acts to seal the alkali in the porous surface of themetal and the outer coatings are merely for better mechanical protectionto preserve the inner coating intact and exclude moisture as far aspossible from it. It is obvious that this method of protecting thesurfaces is much cheaper than The great item ofexpense has been tothoroughly clean and dry the iron surfaces before the paint is applied,because if any minute spots of rust or of moisture remain they will setup rusting beneath the paint. In the present method the iron surfaceneed be cleaned of scale and rust only sufiiciently to allowthe coating,which is put on subsequently to the alkali, to have a good mechanicalgrip on the surface. Thus after the rust which would hinder a goodmechanical bond between the coating and iron, has been brushed off, theremaining rust may be allowed to remain since it is thoroughlyimpregnated with the alkali and is thus rendered absolutely incapable ofsetting up any further rusting.

While any solvent which will take up the alkali may be employed, it isfound that alcohol possesses particularly desirable qualities. Thealcohol, on account of its" low surface tension, very easily permeatesthe surface of the metal and impregnatesit with the alkali, and alcohol,evaporates very rapidly and frees the surface of fluid. A solvent isused' which will entirely evaporate and leave only the alkali. Whilealcohol is preferred because it evaporates very readily,

any other solvent which will evaporate and leave the, alkali maybe used.Ordinary caustic soda or potash, on account of their cheapness, arepreferably used as the alkali. Moreover, both of these alkalis arereadily soluble in alcohol. After the alcohol has evaporated, the actionof the ca'rbondioxid in the air very soon chan es the sodium andpotassium hydrateto sodlum and potassium carbonate which, on. accountoftheir alkaline properties, prevent rust. The particu-. lar reason forapplying the alkali as a hydrate and allowing it to change to acarbonate on the surface is that the hydrates are easily soluble whereasthe carbonates are soluble with great dificulty, particularlyLinalcohol. While any coating may be applied over the alkaline treatedsurface, which is not prejudicially affectedby' the alkali, ordinaryorange shellac is found to serve satisfactorily. The carbonate does notappear to materially afiectthe shellac but if the shellac is appliedover the surface before the by drate is changed to the carbonate, thehydrate turns the shellac to a pinkish color and apparently causes it tobe more brittle al-' though notcausing it to flake or peel. off.

Surfaces to be embedded in codcrcta- If the iron or steel is to be usedin concrete, the concrete in which the iron or steel is embedded may actas the inclosing sheath or binder to prevent the alkali from leaving thesurface. A convenient method of treat-' ing bars to be used in concretereinforcing is to paint them over with a solution of an alkali. Thisimpregnates the surface of the bar with the rust preventing alkali butdoes -not prevent the strong bond which takesmoisture does reach theiron surface the concrete acts to keep the alkali from being washed awayso that the alkali is always present in the pores of the iron toabsolutely prevent the action of rust. Moreover the alkali may be mixedwith the concrete which immediately surrounds the iron bars if theconditions are such that the alkali, requisite to prevent rusting,willnot weaken the con.- crete.

Opposed surfaces of riveted 'or bolted joints which cannot be reachedafter the iron or steel structure is asscmbZcd.-The compound pieces ofstructural iron or steel work, such as girders or posts, are usuallyassembled and riveted at the iron mills. The-opposing surfaces betweenthe riveted pieces must, therefore, be treated before being sent out.The preferred method of treating such surfaces is to brush, mop, orotherwise apply directly to the-surfaces, just before the assemblage ofsuch members, an alkaline bearing substance. A preferred alkalinecoating is a modified form of sappo viridis or green soap which ismodified by an addition of 1 to 2% of a saturated water solution ofcaustic soda or potash. The soap is readily soluble in water and is notprejudicially afiected by the ordinary temperature changes to which itis subjected in forming the joint. If the soap is heated, the oilyconstituents will either be melted'or carbonized, leaving the alkali.The. soap is not volatile or inflammable, is soft enough to be easilyspreadand worked into the surfaces and is thick enoilgh so that it willnot run off. In assembling the iron or steel in place, the surfaces ofthe joints, which care not be reached by the subsequent painting, are tobe likewise treated with the alkaline soap. The edges of the cracks orcrevices of the joint should be calked with shellac or paint so that thealkaline soap is held in place and cannot be washed out by moisture towhich the structure may be subjected. This calking of the cracks may bedone immediately after the joint is finished or may be delayed until thefinal painting of the structure, depending upon the conditions.

The present invention is also applicable to preventing the furtherattacks of rust on structures which have already been attacked. If thesurfaces are exposed, they should be cleaned of paint, rust, or scale,and then treated with an alcoholic solution of alkali and painted overwith an alkali resisting coating. If the surfaces'are such that it isimpossible to reach and clean them mechanically as, for instance, theopposing surfaces of joints in bridge structures or the joints betweenthe plates of ships, an alkaline solution, preferably of alcohol which,because of its low surface tension, will permeate the joint veryreadily, is injected or poured between the surfacesand the edges of thecracks, and the joint subsequently'hermetically sealed up to retain thealkali on the opposed surfaces where it will act to positively check anyfurther inroads of rust.

While the preferred manner of treating the iron and steel surfaces hasbeen specifically described, it is to be understood that consisting ofan alkali and an evaporable solvent, in evaporating the solvent, and inprotecting the treated surface with a coating not prejudicially affectedby the alkali, sub stantially as described.

2. The method of preventing the rusting of iron and steel which consistsin treating the surface to be preserved with an alcoholic solution of acaustic alkali, in evaporating the solvent, and in subsequently coatingthe alkali treated surface with shellac, substantially as described. g

3. The method of preventing the rusting of iron and steel Wl'llCllconsists in treating the surface to be preserved with an alcoholicsolution of an alkaline hydrate, in evaporating the solvent, in exposingthe treated surface to the air to change the hydrate to a carbonate, andin protecting the treated surface with a coating not prejudiciallyaffected by the alkaline carbonate, substantially as described.

DANIEL F. COMSTOCK.

Witnesses:

' HORACE VAN EVEREN,

W. BURTON Wnsco'rr.

